Computer security is becoming increasingly important. Electronic data is valuable not only to the individuals who generated it, but to competitors who want to acquire it. Traditionally, electronic data is protected only by a user ID/password pair. Once the user ID and password become known, data accessible by the user may be compromised.
One well-known way for an information thief to obtain the user ID/password pair is by creating a “Trojan Horse” program that simulates a login screen. The Trojan Horse program may present a login screen to the user and obtain the user ID/password pair when this information is entered by the user. One mechanism that was developed to prevent this scenario is the Secured Attention Sequence (SAS), which guarantees to the user that the login screen is genuine. In one implementation of the SAS, the “Ctrl”, “Alt” and “Del” keys on the keyboard are pressed simultaneously, while using an operating system, such as a Windows NT® operating system from Microsoft Corporation of Redmond, Wash. The Windows NT® operating systems include Windows NT, Windows 2000 and Windows XP from Microsoft Corporation of Redmond, Wash. Using a secured code path, the SAS action notifies the operating system that the user wishes to authenticate himself or herself to the system.
The secured code path is an exclusive access channel to the keyboard device driver. When the operating system boots, it opens an exclusive communication channel to a keyboard driver. No malicious code can be run in the early stage of an operating system boot. Therefore, the operating system has the first chance to secure this communication channel. Once the channel is secured, no malicious code can tap into this channel for snooping on the communication. Any code trying to open a communication channel with the keyboard later will get “access denied” because it is already opened exclusively by the operating system.
In systems, such as those that are executing a Windows NT® operating system, multiple users can be logged onto the system at the same time. Each user has his/her own session and hence is isolated from other users. Each session has at least two desktops, a default desktop accessible by application programs, including a Trojan Horse program, and a secure desktop having a login dialog, accessible only by the operating system.
As a result of the SAS action, the system will display the secure desktop having the genuine login dialog, such as shown in FIG. 3. In the login dialog of FIG. 3, the user is requested to enter his/her username 300, password 302 and domain name 304. Thus, if a Trojan Horse program was running and displaying a login dialog on the default desktop, the SAS action will cause a real login dialog on the secure desktop to be displayed, replacing the false login dialog displayed by the Trojan Horse program. Consequently, the user's ID and password cannot be intercepted by the Trojan Horse program.
Some devices, including but not limited to a Tablet PC, may have input devices other than a keyboard. For example, some of the input devices on the Tablet PC are a pen-shaped stylus and a number of buttons on the case. When such a device does not include a keyboard or the keyboard is folded over or otherwise not available, it is not possible to generate a SAS by pressing keys on a keyboard. Therefore, another method of generating the SAS is needed for such devices.